1. Field of the Invention
The present invention relates to an optical disk drive and a method and a calibration system for setting its write strategy, and more particularly, to a method, a CR-RW drive and a calibration system for adjusting a 2T write strategy to improve recording quality.
2. Description of the Prior Art
As the calculation capability of computers becomes faster and faster and as network technology development progresses rapidly, demand for mass storage devices is rapidly increasing. Devices utilizing optical storage media such as CD-R's (compact disk-recordable) are preferred for such kinds of storage as this media type is more inexpensive, compact, and portable than other types with respect to the same storage capacity. As various kinds of optical disk drives and burners appear with faster speed and more reliable operation, optical disk drives and burners have practically become standard accessories of personal computers. For example, a CD-RW (CD-ReWritable) drive is capable of writing data to a CD-RW disk and erasing the data recorded from the CD-RW disk, thus facilitating data storage for the users.
Generally, when an optical disk drive writes data to an optical disk, the data is transformed into a storage format of the optical disk using an encoder of the optical disk drive. In the prior art, the data transformation is usually referred to an Eight-to-Fourteen Modulation (EFM), which encodes the data to be stored in the optical disk using a square wave of various pulse-widths and intervals along a time axis. The encoded EFM data is recorded onto the optical disk using the optical disk drive. A recording layer within the CD-RW disk is formed of phase-change materials. An optical pick-up unit (OPU) of the CD-RW drive outputs a laser beam onto a predetermined location of the CD-RW disk and activate the portion of the phase-change materials at the predetermined location into an amorphous state or a crystalline state. Since the phase-change materials have different refractive indices respectively in the amorphous state and in the crystalline state, an optical method can be used to distinguish these two states.
The optical pick-up unit of the CD-RW drive mainly provides a bias power Pbias, an erase power Perase, and a write power Pwrite. The write power Pwrite is greater than the erase power Perase, and the erase power Perase is greater than the bias power Pbias. When the CD-RW erases data from the CD-RW disk, the optical pick-up unit of the CD-RW drive outputs the erase power Perase to heat the CD-RW disk and transform the portion of the heated phase-change materials into the crystalline state. When the CD-RW drive writes data onto the CD-RW disk, the optical pick-up unit of the CD-RW drive outputs the write power Pwrite to heat a specific location of the CD-RW disk and followed by outputting the bias power Pbias to cool the CD-RW disk. As a result, the specific location of the CD-RW disk is transformed into an amorphous state and indicates a first logic value “1”. On the contrary, if the optical pick-up unit outputs the erase power Perase to heat the specific location of the CD-RW disk, the specific location is transformed into a crystalline state and indicates a second logic value “0”.
FIG. 1 is a function block diagram of a CD-RW drive 10 according to the prior art. The CD-RW drive 10 comprises an optical pick-up unit 12, a power control unit 14, a controller 16 and a memory 18. The optical pick-up unit 12 is capable of outputting laser beams with different powers onto an optical disk according to different driving voltages. For example, the optical pick-up unit 12 is capable of outputting a bias power Pb, an erase power Pe, and a write power Pw. The power control unit 14 controls the output power of the optical pick-up unit 12. For example, during an erasing operation, the power control unit 14 supplies an appropriate driving voltage to the optical pick-up unit 12, so as to control the optical pick-up unit 12 to output the erase power Pe. The controller 16 executes the firmware 20 stored in the memory 18 to control the entire operation of the CD-RW drive 10. For example, during a data writing operation, the controller 16 outputs control signals to the power control unit 14, so as to drive the power control unit 14 to supply the appropriate driving voltage to the optical pick-up unit 12. In practical application, the CD-RW drive 10 uses a write strategy to control the output power of the optical pick-up unit 12 for burning marks corresponding to the EFM data onto a CD-RW disk correctly. The write power Pw and the bias power Pb are alternately outputted from the optical pick-up unit 12 to burn marks with specific lengths (corresponding to the amorphous state) to store a predetermined logic value on the CD-RW disk.
As is well known in the art, a 1T write strategy is usually used for a low-speed data writing operation, such as 16x (x means writing speed), to store the EFM data. In a base period (1T) of the EFM clock, the optical pick-up unit 12 may output the write power Pw once. However, as the burning technology of the optical storage device increases, more and more CD-RW drives with higher writing speeds appear (for example, CD-RW drives of 32x or 48x writing speed), the EFM base period has become shorter and shorter so that time in the base period (1T) for outputting the base power Pb after the optical pick-up unit 12 outputs the write power Pw is not long enough to cool the phase-change materials to record the logic value. Therefore, high-speed writing operation may have problems such as insufficient time for outputting the base power and cooling the phase-change materials, and may even result in data errors.
In order to solve the problems of the 1T write strategy, the prior art develops a 2T write strategy. Please refer to FIG. 2 and FIG. 3. FIG. 2 is a schematic diagram of using a 2T write strategy to form an even mark according to the prior art, and FIG. 3 is a schematic diagram of using a 2T write strategy to form an odd mark according to the prior art. As is well known in the art, the EFM data is transformed into marks with different lengths and stored on a CD-RW disk. According to the specification (Orange Book Part III, Volume 3), when the 2T write strategy is used, the marks with different lengths include even marks and odd marks. The even marks include a 2T mark, a 4T mark, a 6T mark, an 8T mark and a 10T mark. The odd marks include a 3T mark, a 5T mark, a 7T mark, a 9T mark and an 11T mark.
As shown in FIG. 2, when the controller 16 uses the 2T write strategy to form a 10T mark on a CD-RW disk, the controller 16 has to drive the power control unit 14, and the power control unit 14 subsequently drives the optical pick-up unit 12 to output the erase power Pe. The controller 16 then drives the power control unit 14 at time t to set the optical pick-up unit 12 to continuously output the write power Pw during a writing period Tmn. Following that, the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the bias power Pb. Obviously, the optical pick-up unit 12 outputs the write power Pw to heat the phase-change materials in the CD-RW disk, and the phase-change materials is cooled when the optical pick-up unit 12 varies to output the bias power Pb. As illustrated in the waveform shown in FIG. 2, the optical pick-up unit 12 continuously outputs the write power Pw during the writing period Tmn in each 2T period. After the optical pick-up unit 12 completes to output the write power Pw during the writing period Tmn at the last 2T period (8T-10T), the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the bias power Pb during a cooling period Tc1. Thereafter, the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the erase power Pe to complete the formation of the 10T mark. Methods for forming other even marks are similar to the method for forming the 10T mark. Take a 4T mark as an example, after two outputs of the write power Pw in the period of 0-4T, the optical pick-up unit 12 subsequently outputs the bias power Pb during the cooling period Tc1 and then outputs the erase power Pe to complete the formation of the 4T mark.
As shown in FIG. 3, when the 2T write strategy is applied to form an 11T mark on a CD-RW disk, the controller 16 has to drive the power control unit 14, and the power control unit 14 subsequently drives the optical pick-up unit 12 to output the erase power Pe. The controller 16 then drives the power control unit 14 at time t to set the optical pick-up unit 12 to continuously output the write power Pw during a writing period Tmn. Following that, the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the bias power Pb. Obviously, the optical pick-up unit 12 outputs the write power Pw to heat the phase-change materials in the CD-RW disk, and the phase-change materials is cooled when the optical pick-up unit 12 varies to output the bias power Pb. As shown in FIG. 3, except in the last three base periods (9T-11T), the optical pick-up unit 12 continuously outputs the write power Pw during the writing period Tmn in each 2T period. After the optical pick-up unit 12 completes the output of the write power Pw during the last writing period Tmn in the period of 6T-8T, the controller 16 drives the power control unit 14 at time t′ to set the optical pick-up unit 12 to continuously output the write power Pw during a writing period Tmn+. Following that, the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the bias power Pb during a cooling period Tc2. Finally, the controller 16 drives the power control unit 14 to set the optical pick-up unit 12 to output the erase power Pe to complete the formation of the 11T mark. Methods for forming other odd marks are similar to the method for forming the 11T mark. Take a 5T mark as an example, after an output of the write power Pw in the time period of 0-2T, the optical pick-up unit 12 subsequently outputs another write power Pw during the following 3T period. Then, the optical pick-up unit 12 outputs the bias power Pb during the cooling period Tc2 and then outputs the erase power Pe to complete the formation of the 5T mark.
According to the 2T write strategy described above, the write power Pw is used to heat the CD-RW disk once in each 2T period. Therefore, the time interval between two heating operations using the writing power Pw is enough to cool the phase-change materials and transform the phase-change materials into the amorphous state at high-speed writing operation. For the odd mark and the even mark, the heating period thereof is corresponding to the same value. As a result, the heating periods Tmn and Tmn+ may be long enough for the portion of the phase-change materials in a first predetermined length (the odd mark) to be transformed uniformly into the amorphous state, but the heating period Tmn is not long enough for the portion of the phase-change materials in a second predetermined length (the even mark) to be transformed uniformly into the amorphous state. In other words, when the optical pick-up unit 12 reads the marks recorded on the CD-RW disk, the RF signals associated with the odd mark may form a better waveform, and the RF signals associated with the even mark may form an improper waveform. Similarly, when forming the even mark, the heating period Tmn may uniformly transform the portion of the phase-change materials with a first predetermined length into the amorphous state. However, when forming the odd mark, the same heating period Tmn and the adjustable heating period Tmn+ may not uniformly transform the portion of the phase-change materials with a second predetermined length into the amorphous state. In other words, when the optical pick-up unit 12 reads the marks recorded on the CD-RW disk, the RF signals associated to the even mark may form a better waveform, and the RF signals associated to the odd mark may form an improper waveform.
To sum up the 2T write strategy as mentioned in the above paragraphs, the heating period Tmn for forming the odd mark and the heating period Tmn for forming the even mark are referred to the same value according to the prior art, and the heating period Tmn+ is only used for forming the odd mark. Therefore, the heating period Tmn, which forms the odd mark with high recording quality, does not certainly form the even mark with high recording quality. Similarly, the heating period Tmn, which forms the even mark with high recording quality, does not certainly form the odd mark with high recording quality. As a result, it is not easy for the CD-RW drive 10 to form both of the odd mark and the even mark with high recording quality using the prior art 2T write strategy.